The VK9 monoclonal antibody recognizes human Globo H, a hexasaccharide formed from the pentasaccharide precursor, SSEA3 (stage-specific embryonic antigen 3). It is a member of a family of antigenic carbohydrates expressed on the surface of cancer cells as glycolipids and possibly glycoproteins. Globo H is overexpressed on many carcinomas, such as breast, colon, ovarian, gastric, pancreatic, lung, and prostate. Expression is observed in more than half of all ductal, lobular, and tubular breast carcinomas, but not in non-epithelial breast tumors. Globo H is also expressed on cancer stem cells and human embryonic stem cells, although expression decreases when cells are differentiated toward both neural progenitor cells and to a lesser extent in endodermal lineage cells. Expression in normal tissues is limited to cells composing secretory borders. Globo H is considered a target for immunotherapy of many epithelial cancers.